Formulations and blends comprising polycarbonates are known to degrade upon prolonged exposure to sunlight or other forms of light. One of the effects observed is yellowing of the polycarbonate blend/formulation. This problem has been partially alleviated by the use of light absorbers or light blockers in the polycarbonate blends. Thus ultraviolet light absorbers (UVA) are known to be used in polycarbonate formulations to protect these formulations from degradation due to exposure to different sources of light.
It has been known that aliphatic polyesters are resistant to light induced photo-yellowing in particular, because they do not absorb light wavelengths normally encountered in outdoor exposure. Blends of polycarbonates and poly(1,4-cyclohexanedimethanol-1,4-cyclohexanedicarboxylate) (PCCD) have been studied and reported in Polymer International, 36, 127 (1995) and the Journal of Physics: Condensed Matter, 8, 311 (1996). However, their photostability has not been examined.
The use of light stabilizing additives, UVA's in particular, to improve the photostability of polymers is known. Use of UVA's, however, does not offer a complete protection of polycarbonate formulations from light induced degradation or discoloration. There is thus a continued need for a formulation that will help protect polycarbonate based formulations/blends from degradation or discoloration due to exposure to light.
It has been surprisingly found that use of at least one of a benzotriazole, benzophenone, and a triazine based UVA, in compositions comprising polycarbonate and cycloaliphatic polyester resins exhibits a synergistic effect and, affords enhanced protection and increased weatherability, to the polycarbonate compositions against light induced degradation. This synergistic increase in weatherability, is greater than the additive protective effect of the polyester resin and the UVA. The protection afforded is generally measured in terms of the Yellowness Index (YI). Improvements in retention of gloss and mechanical properties are also expected.